This invention relates to conduit sections and more particularly to an adapter for providing a transition between a conduit section to at least one single bore pipe.
With the increasing use of transmission lines, such as telephone and telegraph cables, computer data lines and cable television, as well as public protestations against above ground transmission towers, underground burial of cables has become the expedient used to provide a path for such cables. The use of buried conduit sections to provide cable passages not only overcomes public dissatisfaction with above ground installations, but also provides an economical way of expanding capacity without a great increase in capital costs required by erecting new transmission towers or gaining access to new rights of way. By initially installing conduit sections having capacity above the present requirements, the excess conduit passages may be used for later growth by merely drawing new cables therethrough.
Several cable conduits have been proposed in the past, such as those disclosed in commonly assigned U.S. Pat. Nos. 3,545,493, 3,792,878 and copending, commonly assigned U.S. Patent application Ser. No. 403,248 filed Oct. 3, 1973.
In the past, there have been problems in providing a smooth transition between the generally rectangular passageways in cable conduits to a cylindrical pipe. It is frequently desirable to provide a sealed connection between a plurality of single bore pipes to a multi-passage conduit section. In prior art adapters, the joint between the adapter and the conduit section would fail when subjected to substantial shear stress, as when ground settles resulting in void areas beneath the conduit. Whereas partition walls in the adapter and the adjacent conduit section function to reinforce the sidewall of the conduit, they provide little if any support for the joint.
With increasing depths of burial and increasing conduit widths, greater pressure is presented on the conduit and adapter particularly at the joints therebetween. In prior art types of adapters, one end of the adapter is a spigot which is receivable in the bell end of an adjacent conduit section, and the shear stress at the joint with the conduit is supported mainly by the bell of conduit. As the width of the adapter and conduit are increased, the pressure thereon is increased as by ground loads of heavy vehicles above the adapter and conduit, and the bell is often over stressed and failures have occurred which may result in damage to the integrity of the adapter and conduit and damage to the cables positioned therein.